Revelation 9:11
Revelation 9:11 And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.
Textus Receptus
καὶ ἔχουσιν ἐφ' αὐτῶν βασιλέα τὸν ἄγγελον τῆς ἀβύσσου ὄνομα αὐτῷ Ἑβραϊστὶ Ἀβαδδὼν, καὶ ἐν τῇ Ἑλληνικῇ ὄνομα ἔχει Ἀπολλύων.
In the King James Version of 1611, it has a footnote at the word Apollyon which says:
"That is to say A destroyer".